Price....
Expecting the 10-18mm to be twice the price of the 18-55mm - due to a smaller market, than the kit lens
Expecting the 16-35mm f4 IS to start just a tad more costly than the 16-35mm f2.8 II, dropping to about 4/5th's of the price, then a new 16-35mm f2.8 III coming in at nearly twice the price of the f4.0 in about 12 months... Both as sharp as current primes